The present invention relates to a control method and system for improving the color temperature of an alternating current (AC) plasma display panel (PDP), and more particularly, to a method and apparatus for controlling the color temperature of an AC PDP, which is capable of maintaining high luminance and luminous efficiency even in an XGA class discharge cell as well as a VGA class discharge cell because a discharge space is dispersed from a sustain electrode to the direction of a writing electrode, to thus obtain strong sustain discharge having a large discharge space when a pulse is simultaneously applied to the writing electrode while a sustain pulse waveform is applied during a sustain period of the AC PDP, of improving only the bright of a blue cell whose luminance is relatively low regardless of a cell structure because different pulses can be independently applied to the writing electrodes of red, blue, and green cells during the application of the sustain pulse, and of controlling a color temperature by increasing the luminance of the blue and green cells. As a result, it is possible to improve the color temperature of a white cell in a state of high luminance.
FIG. 1A is a perspective view illustrating upper and lower substrates of a common alternating current (AC) surface discharge PDP, which are separated from each other. FIG. 1B is a plane view illustrating the upper and lower substrates of an AC PDP, which are separated from each other. The AC surface discharge PDP includes a front substrate 1 for displaying information and a back substrate 2 having the same width as that of the front substrate 1 and positioned to be parallel to the front substrate 1.
The front substrate 1 includes a plurality of sustain electrode lines X and Y including transparent electrodes 6 and bus electrodes 7 having low resistivity, the sustain electrode lines X and Y for applying a voltage waveform, a dielectric layer 8 formed between sustain electrode lines, the dielectric layer 8 for restricting discharge current, and a protective layer 9 formed on the dielectric layer 8, the protective layer 9 for protecting the sustain electrode lines. The back substrate 2 includes a plurality of partitions 3 forming a discharge space, a plurality of writing electrode lines 4 formed to be perpendicular to the sustain electrode lines between the partitions 3, and a fluorescent film 5 whose discharge spaces are formed to wrap the corresponding writing electrode lines 4 on both partition surfaces and a back substrate, the fluorescent film 5 for receiving vacuum ultraviolet (VUV) generated during discharge and emitting a visible ray.
FIG. 2A is an entire driving waveform chart illustrating waveforms applied to the respective electrodes X, Y and Z during a sub field in a conventional AC PDP. FIG. 2B is an enlarged waveform chart for a sustain pulse.
FIG. 2A illustrates an example of voltage waveforms applied to the sustain electrode lines X and Y formed of the transparent electrodes 6 and the bus electrodes 7 of FIG. 1 in order to display information on the AC PDP and the writing electrode lines 4. A time can be divided into an erase period T1, a write period T2, and a sustain period T3. During the erase period T1, a wall charge that becomes uneven while the AC PDP displays previous information becomes even over an entire panel by alternately applying a low lamp type pulse and a high pulse to the sustain electrode lines X and Y as illustrated in FIG. 2A. During the write period T2, information is written by accumulating a wall charge after writing discharge only on a cell to be displayed by a voltage difference between the sustain electrode line X and the writing electrode line Z. During the sustain period T3, information is displayed by alternately applying a voltage to both sustain electrode lines X and Y and making a visible ray emitted only from the cell, into which information is written during the write period T2.
In a common AC PDP, the waveforms of the X and Y pulses that are both sustain electrode lines are square waves in the sustain period T3. A voltage is not applied to the writing electrode. FIG. 2B illustrates enlarged waveforms applied to the respective electrodes for a time, for which a sustain pulse is applied. T4 denotes a rest period, during which no voltage is applied to all of the electrodes. In T5, the moment a voltage of a square wave is applied to the sustain electrode X and discharge starts, a visible ray is emitted for a short time. After a rest period T6, when a square wave is applied to the sustain electrode Y, discharge occurs and a visible ray is emitted. At this time, no voltage is applied to a writing electrode Z.
Among three primary colors of red R, green G, and blue B used by the common AC PDP in order to express an image, blue is emitted so that the intensity of light is weaker than the intensity of those of green and red due to the characteristic of a discharge gas such as Ne. Accordingly, the AC PDP has a low color temperature. Therefore, in order to use the AC PDP as a commonly used display device, the color temperature must be raised. Accordingly, various methods for raising the color temperature of the AC PDP are provided.
FIGS. 3A to 3C illustrate one of conventional methods for raising the color temperature of the AC PDP by gamma-correcting an analog video signal. Generally, an analog video signal input from the AC PDP is digitalized in 256 luminance steps from 0 to 255 in each color in order to realize gray scales and is expressed by the number of sustain pulses. The analog video signal input to the AC PDP is not corrected in consideration of the characteristic of the AC PDP but is a signal, in which red, green, and blue have the same peak value. In a conventional technology, in order to raise the color temperature of the PDP, as shown in FIGS. 3A to 3C, red (FIG. 3A) and green (FIG. 3B) analog video signals excluding a blue (FIG. 3C) analog video signal having relatively low luminance are inverse gamma corrected so that a peak value of each color is lowered before a digitalizing step and are digitalized. After such a step, the number of sustain pulses having the maximum luminance of red and green is smaller than the number of sustain pulses having the maximum luminance of blue. Accordingly, the color temperature can be raised. For example, if 255 sustain pulses are used for expressing the maximum luminance of blue, the maximum luminance is expressed by about 200 sustain pulses in the case of green and by about 180 sustain pulses in the case of red.
In the conventional method of raising the color temperature, because all of the 255 sustain pulses required for expressing the maximum luminance of green and red are not used, it is disadvantageous to realizing gray scales. As a result, a step phenomenon occurs in red and green in expressing an image that becomes gradually bright or dark.
FIGS. 4A and 4B are views for explaining another method among conventional technologies used for raising the color temperature of the AC PDP. A method of raising the color temperature using uneven partitions is shown. Distance between partitions of a common AC PDP is uniform so that red, green, and blue have discharge spaces of the same width as shown in FIG. 4A. The red, green, and blue cells are combined with each other, to thus form a pixel. When the distance between partitions in a part for displaying a specific color is widened, a discharge space is widened and thus, strong discharge is obtained. Accordingly, it is possible to obtain higher luminance than other colors. A method of raising the color temperature of the AC PDP using the above phenomenon is the method using the uneven partitions shown in FIG. 4B. That is, as illustrated in FIG. 4B, the distance between the partitions of blue having relatively lower luminance than red and green is widened. In order to sustain the size of a pixel to be uniform, the distance between the partitions of red and green is narrowed. Therefore, the discharge space of blue is widened and thus, strong discharge and high luminance can be obtained. The discharge spaces of red and green are narrowed and thus, weak discharge and low luminance are obtained.
The above-mentioned step phenomenon does not occur because the 255 sustain pulses are used for expressing the maximum luminance of each color. During write discharge or sustain discharge, non-uniformity of discharge occurs due to the discharge spaces different from each other according to colors. Accordingly, mis-discharge occurs and a voltage margin for stable driving is reduced. Also, according to the method, the color temperature is increased by changing the structure of a cell. Therefore, once the structure is fixed, a color temperature is fixed though the color temperature is high. Accordingly, it is not possible to realize a function of controlling a color temperature, which high quality video display devices have.
To solve the above problem, it is an object of the present invention to provide a control method and system for selectively increasing the luminance and the luminous efficiency of a blue cell of an alternating current (AC) plasma display panel (PDP) regardless of a symmetrical cell structure or an asymmetrical cell structure, which is capable of increasing the luminance and the luminous efficiency of an XGA class AC PDP as well as a VGA class AC PDP and of selectively increasing the luminance of a blue cell whose luminance is relatively low by applying a pulse to a writing electrode while a sustain pulse is applied to a sustain electrode. Thus, sustain discharge is performed and by enlarging the discharge space of a selected cell, the luminance and the efficiency are increased.
It is another object of the present invention to provide a control method and apparatus for raising the color temperature of an AC PDP, which is capable of controlling the color temperature in a state where the luminance is not lowered, to thus raise the color temperature, by simultaneously applying pulses having appropriate width and height to writing electrodes of green and blue cells that can contribute to raising the color temperature through various methods while the sustain pulse is applied and the sustain discharge is performed.
To achieve the above objects, in one aspect of the present invention, there is provided a control method for enhancing a color temperature of an alternating current type plasma display panel which includes a plurality of pixels for implementing a color image, a plurality of discharge cells having at least one color in the respective pixel, and a maintenance time period for driving, and displays image data by inducing discharge of the plurality of cells through a plurality of sustain electrodes and writing electrodes, the method comprising the steps of a) inducing a sustain discharge between the sustain electrodes of the respective cells by applying a sustain pulse according to the image data and b) applying a control pulse having a predetermined voltage to the writing electrode of at least one discharge cell of the plurality of discharge cells with different colors so as to independently control a luminance of the respective discharge cells with different colors for the sustain pulse is continuously applied.
Preferably, the colors are red (R), green (G), and blue (B), and the step b) includes the sub-step of applying the control pulse having the predetermined voltage to a writing electrode for the blue (B).
According to the features of the present invention, the step b) includes the sub-step of applying the control pulse having the predetermined voltage to a writing electrode for the green (G) independently with the control pulse applied to the writing electrode for the blue (B).
Preferably, the step b) includes the sub-step of applying the control pulse having the predetermined voltage to a writing electrode for the red (R) independently with the control pulses applied to the writing electrodes for the blue (B) and green (G).
Preferably, the control pulse is applied simultaneously with when the sustain pulse is applied.
Preferably, the appliance of the control pulse is delayed as much as a time interval between the sustain pulse is applied and a predetermined time.
Preferably, the control pulse is comprised of at least one pulse array when the sustain pulse is continued.
Preferably, the step b) adjusts the voltage of the control pulses applied to the respective writing electrodes of the discharge cells with different colors according to the color temperature required to the plasma display panel.
Preferably, the step b) adjusts the time-axial position of the control pulses applied to the respective writing electrodes of the discharge cells with different colors according to the color temperature required to the plasma display panel.
Preferably, the step b) adjusts the voltage of the control pulses applied to the respective writing electrodes of the discharge cells with different colors according to the color temperature required to the plasma display panel.
In another aspect of the present invention, there is provided a controlling apparatus for enhancing color temperature of an alternating current type plasma display panel, which includes a plurality of pixels for implementing a color image, a plurality of discharge cells having at least one color in the respective pixel, and a maintenance time period for driving, and displays image data by inducing discharge of the plurality of cells through a plurality of sustain electrodes and writing electrodes, the apparatus comprising a sustain pulse circuit for inducing a sustain discharge between the sustain electrodes of the respective cells by applying a sustain pulse according to the image data, and a color temperature controlling circuit for applying a control pulse having a predetermined voltage to the writing electrode of at least one discharge cell of the plurality of discharge cells with different colors so as to independently control a luminance of the respective discharge cells with different colors for the sustain pulse is continuously applied.